Caliber reference
Seiko NH70 (TMI NH70A) caliber: dimensions and drop-in group
The published footprint of the Seiko NH70 (TMI NH70A) and which movements share it.
Used in: the fully skeletonised member of the NH3x family, in open-worked mod watches.
A fully skeletonised NH3x caliber at 27.40 mm x 5.32 mm, sharing the family footprint and stem but designed to be seen through the dial. It needs a skeleton dial and has no seconds hand or date; the NH72 is its hacking, hand-winding sibling.
Drop-in group: Seiko NH70 / NH72 skeleton footprint (27.40 mm x 5.32 mm). Matching diameter and height is necessary but not sufficient. A donor is only a true drop-in when the dial-foot positions, hand-hole sizes, stem length and calendar layout also match. Two movements can share a case and still need a new dial, re-broached hands or a cut-to-length stem.